| Hydrocyclones offer a simple, cost-effective
way to separate solids or gases from liquids
or to separate liquid mixtures. Like
a centrifuge, a hydrocyclone separates mixtures based
on the differential densities of the mixture
fractions.
However, UNLIKE centrifuges, hydrocyclones...
- have no moving parts
- require no separate power source
- require less maintenance - none
at all in some applications
- have modest prices that make
them affordable for many industrial
processes
Because of these characteristics, they are generally
reliable, cost-effective, energy-efficient devices that are simple to
install and effective in operation.
How They Work - a simplified
explanation
A pump or other external pressure
source causes the liquid mixture to flow through the
hydrocyclone.
The mixture enters tangentially and spins in the
cylindrical entrance to the hydrocyclone.
Spinning causes the heavier
fraction to be thrown toward the wall of the chamber.
This fraction continues on a downward spiral path
at the
tapered wall to an outlet at
the bottom apex. This outlet is known as the
underflow.
The less dense fraction moves in
the opposite direction, spiraling upward
on the axis of the hydroclone toward an outlet at
the hydroclone's top center.
This outlet is known as the
overflow.
Construction
ChemIndustrial makes hydrocyclones
in both 316L stainless steel and
chemical-resistant polypropylene. ChemIndustrial's clamped flange modularity allows great
flexibility in hydrocyclone configuration, including...
- several inlet geometry choices
- extended body lengths
to increase separation time
- right and left-handed models
- simple integration of heavies
handling options such as accumulation chambers and
automatic valves
Clamps
are 304 Stainless while gaskets are either EPDM or Viton®.
If customers require a hydrocyclone skid, the frame
is usually built from 304 Stainless tube.
Skid pipework is available in polypro or 316L stainless.
Other materials may be available on special order.
Hydrocyclone Arrays
Multiple hydrocyclones can be manifolded into...
- parallel arrays for higher flow rates
- valved parallel arrays to allow
manual or automatic rate adjustment
- series arrays for multistage or multiphase recovery
Limitations
Hydrocyclones are surprisingly
effective at separating mixtures into heavy and
light fractions.
However, they are not perfect separators. Here's
a discussion of
some of the limitations and some ways of dealing with
them:
- Hydrocyclones don't work for
all separations.
- Even when hydrocyclones work
well, it is rare for them to achieve perfect
separation. Expect some heavies in the
overflow and always some lights in the underflow.
- Hydrocyclones are not good at
handling variable flow rates. The reason is
that flow variations cause the spin rate in the
hydrocyclone to vary. This leads to variation
in the g-force that drives the separation.
The best way to combat this problem is to run each
hydrocyclone at a constant flow rate which is also
the optimum flow rate for the separation task.
If the rate must vary, the proper strategy is to
install multiple smaller valved hydroclones instead
of a single larger one and turn the small ones on
and off as required to satisfy the current flow.
ChemIndustrial's staged valved parallel arrays of
hydroclones provide a way to address this problem.
- Underflow issues:
- Variation in the
percentage of heavies leads to less efficient
separation. This
is because the underflow orifice must be big
enough to flow all of the separated heavy
material at maximum heavies concentration.
When the heavies concentration is less, the
orifice still passes the same volume with extra
light material making up the difference.
ChemIndustrial may be able to provide process
control solutions to this problem where cost
is justified.
- Low concentration of
solid heavies requires the underflow orifice to
be very small. This can lead to bridging
and plugging of the orifice.
An accumulation chamber can address this problem by providing
an engineered semi-isolated holding zone for "heavies".
The accumulation chamber can be discharged periodically
by a timed blowdown cycle, or under the control of
a turbidimeter or other sensor.
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